Visible Light Mediated Activation and O-Glycosylation of Thioglycosides

In situ SERS monitored photoactive yellow protein (PYP) chromophore model elimination, nano-catalyzed phenyl redox and I2 addition reactions

PhS nitration products absorbed on Ag/Au NPs underwent nitro- and amino-group redox cycle reactions monitored using SERS spectra. I₂ addition to the CC double bond was also confirmed with SERS.

Light-driven highly efficient glycosylation reactions

A novel and efficient light-driven glycosylation strategy was developed with wide substrate scope/generality.

Recent synthetic additions to the visible light photoredox catalysis toolbox

The boom in visible light photoredox catalysis (VLPC) research has demonstrated that this novel synthetic approach is here to stay. VLPC enables reactive radical intermediates to be catalytically generated at ambient temperature, a feat not generally allowed through traditional pyrolysis- or radical initiator-based methodologies. VLPC has vastly extended the range of substrates and reaction schemes that have been traditionally the domain of radical reactions. In this review the photophysics background of VLPC will be briefly discussed, followed by a report on recent inroads of VLPC into decarboxylative couplings and radical C-H functionalization of aromatic compounds. The bulk of the review will be dedicated to advances in synergistic catalysis involving VLPC, namely the combination of photoredox catalysis with organocatalysis, including β-functionalization of carbonyl groups, functionalization of weak aliphatic C-H bonds, and anti-Markovnikov hydrofunctionalization of alkenes; dual catalysis with gold or with nickel, photoredox catalysis as an oxidation promoter in transition metal catalysis, and acid-catalyzed enantioselective radical addition to π systems.

A propos of glycosyl cations and the mechanism of chemical glycosylation; the current state of the art

An overview of recent advances in glycosylation with particular emphasis on mechanism is presented. The mounting evidence for both the existence of glycosyl oxocarbenium ions as fleeting intermediates in some reactions, and the crucial role of the associated counterion in others is discussed. The extremes of the SN1 and SN2 manifolds for the glycosylation reaction are bridged by a continuum of mechanisms in which it appears likely that most examples are located.

Photo-induced glycosylation using reusable organophotoacids

The glycosylation reactions of glycosyl trichloroacetimidates and several alcohols using an organophotoacid as an activator under photoirradiation proceeded smoothly to give the corresponding glycosides in high yields. The organophotoacid was recovered and reused without any loss of efficiency.

An air- and water-stable iodonium salt promoter for facile thioglycoside activation

The air- and water-stable iodonium salt phenyl(trifluoroethyl)iodonium triflimide is shown to activate thioglycosides for glycosylation at room temperature. Both armed and disarmed thioglycosides rapidly undergo glycosylation in 68–97% yield. The reaction conditions are mild and do not require strict exclusion of air and moisture. The operational simplicity of the method should allow experimentalists with a limited synthetic background to construct glycosidic linkages.

Light-induced O-glycosylation of unprotected deoxythioglycosyl donors

The O-glycosylation of several unprotected deoxythioglycosides and alcohols using 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) under long-wavelength UV irradiation was effectively realized using a single electron transfer (SET) mechanism. In some cases, the use of p-methoxyboronic acid was very effective in temporary protection of the 1,3-diol (C4 and C6 positions) of the unprotected glycosyl donors to increase the yields of the obtained O-glycosides.

Visible Light Photocatalysis: The Development of Photocatalytic Radical Ion Cycloadditions

Photochemistry has the potential to significantly impact multiple aspects of chemical synthesis, in part because photoinduced reactions can be used to construct molecular architectures that would otherwise be difficult to produce. Nevertheless, organic chemists have been slow to embrace photochemical synthesis because of technical complications associated with the use of ultraviolet light. Our laboratory has been part of an effort to design synthetically useful reactions that utilize visible light. This strategy enables the synthesis of a diverse range of organic structures by generation of a variety of reactive intermediates under exceptionally mild conditions. This Perspective article describes the reasoning that led to the conception of our first experiments in this area, the features of our reaction design that have been most powerful in the discovery of new processes, and a few of the possible future areas in which visible light photocatalysis might have a large impact.